SSA field and on change script

Is it possible to use an on change script with a search select advanced field?  When I attempt this, I loose my SSA selection list.

Based on the selection in the SSA field (which is an address record), I want to populate the value of other fields on the screen.

This is on an opportunity record.  The SSA field represents a project location id.  Therefore, I want to populate the project address in other fields (address, city, state, zip).

What is the best way to achieve this?

Any assistance would be greatly appreciated.  Thank you!